Anti-blocking hydraulic brake system

ABSTRACT

An external energy source of a hydraulic motor vehicle power brake system, which has first and second valves that can be electrically controlled to adjust wheel brake pressures for wheel brakes, must be protected from being overloaded. To avoid the necessity for a safety valve, which has been used up to this point for protecting the external energy source, it is proposed that the first valve be embodied as a seat valve having a valve seat connected to the external energy source by means of an inlet opening disposed upstream, having a valve closing body associated with the valve seat, and having a closing spring that presses the valve closing body against the valve seat, which spring is dimensioned as a safety valve spring in a fashion according to the invention. In a reasonably priced manner, the first valve is used as a safety valve that protects the external energy source and on the other hand, for braking procedures, is used as a valve for adjusting wheel brake pressures.

PRIOR ART

The invention is based on a hydraulic motor vehicle power brake systemwith at least one valve that can be electrically controlled.

The document U.S. Pat. No. 3,802,745 has disclosed a hydraulic motorvehicle power brake system having a reservoir, a pump, a pump pressureregulating valve, and at least one external energy reservoir that can befilled by the pump. The reservoir is embodied as a hydraulic accumulatorequipped with a dividing membrane and is provided with a buffer gasfilling, and a valve device between the external energy reservoir valvedevice which valve device can be electrically controlled and is forconnecting at least one wheel brake to the external energy reservoir. Awheel brake pressure sensor is associated with the at least one wheelbrake, and a brake pedal have a potentiometer as a set-point transmitterfor a wheel brake pressure in which the potentiometer can be adjusted bymeans of the brake pedal. A control device is connected to the set-pointtransmitter and the wheel brake pressure sensor and is equipped tocontrol the valve device in such a way that by connecting the at leastone wheel brake to the external energy source, it is possible toincrease the wheel brake pressure until the set point is attained and byconnecting the wheel brake to the reservoir, it is possible to reducethe wheel brake pressure when the brake pedal is released. This valvedevice, which is of a type that is known per se and is therefore notdescribed, has three connections. For example, it is possible to providea number of these valve devices so that for example, each wheel brake ofeach individual wheel of the vehicle has its own valve device. Bydisposing wheel rotation sensors and modifying the control device, it ispossible to adjust brake pressures toward a set-point predetermined bythe brake pedal so that a locking of vehicle wheels is prevented. Thetechnical expenditure for the pump pressure regulator valve, whichconducts excess supplied pressure fluid to the reservoir when the pumpis driven, the hydraulic accumulator is fully charged, and the brakepedal is not being actuated, can be seen as disadvantageous.

A hydraulic motor vehicle power brake system disclosed by DE 19 61 039A1 differs from the hydraulic motor vehicle power brake system accordingto U.S. Pat. No. 3,802,745, which is mentioned above, by the eliminationof a pump pressure limiting valve and the installation in its place, ofa pressure switch for turning off an electromotor, which drives thepump, when the external energy reservoir is sufficiently charged. Thedisposition of the pressure switch and the electromotor has on the onehand the advantage that the pump only operates until the external energyreservoir is sufficiently filled. On the other hand, though, thedisposition of this kind of pressure switch has the disadvantage thatwhen a possibly inevitable welding of contact elements occurs, theelectromotor can no longer be switched off, which results in theoverloading or complete destruction of the electromotor, the pump, orother components of the motor vehicle power brake system. Aside from theuse of valves with three connections between the external energy source,a wheel brake cylinder, and the reservoir, DE 19 61 039 A1 alsodiscloses the disposition of an electromagnetically controllabledirectional control valve between the external energy source and thewheel brake cylinder, which valve is provided with two connections andcan be adjusted for two positions, and also discloses the disposition ofa second 2-connection-2-position directional control valve between thiswheel brake cylinder and the reservoir. Both 2-connection valves areequipped with closing springs and are closed in their normal positions.

In a vehicular brake system that can be operated with external energy,DE 40 29 793 A1 has disclosed the embodiment of necessary 2/2-wayvalves, which are designated for adjusting wheel brake pressures withthe aid of wheel brake pressure sensors, as seat valves in order toprevent leakage flows. This increases the operational safety of themotor vehicle power brake system particularly when in the event of afailure of the external energy, braking function has to be producedthrough the use of a master cylinder that can be actuated by means of apedal.

ADVANTAGES OF THE INVENTION

The hydraulic motor vehicle power brake system according to theinvention has the advantage that installation of a pump pressureregulating valve, as is taught by U.S. Pat. No. 3,802,745, can beeliminated because the spring embodied according to the invention,together with the closing member and the valve seat, which is connectedto the external energy source and is part of the valve used for braking,assumes the function of a pump pressure regulating valve, at least whenthe brake pedal is not actuated. If in spite of, a pressure switchaccording to DE 19 61 039 A1 that is associated with an electromotorthat drives the pump, then the electromotor and the pump of the powerbrake system are spared between braking procedures. This also savesenergy.

Advantageous modifications and improvements of the hydraulic motorvehicle power brake system are possible by means of the measures takenherein.

The features set forth herein produce the advantage that a wheel brakepressure can at least be reduced by at least partially permitting thebrake pedal to move back in the direction of its initial position.

The features set forth herein produce the advantage that due to anadjustment of the pressing of the second closing body against the valveseat of the second valve body because of the controlled or regulatedadjustment of the second excitation current, it is possible for pressurefluid to be discharged to the reservoir while maintaining the firstexcitation current during a braking procedure. The external energysource delivers excess pressure fluid, which results in the fluidflowing through the first valve seat. In so doing, in a manner thatsupports the invention, fluid can flow through the valve seat of thesecond valve so that the external energy source can be protected againstoverloading.

The features set forth herein produce the advantage that for example anumber of vehicle wheels can be braked independently of one another sothat for example, as has already been taught by U.S. Pat. No. 3,802,745,with the disposition of wheel rotation sensors and a modification thecontrol device, the danger of wheel locking in one or several vehiclewheels can be prevented individually by means of operationally dependentautomatic reduction of wheel brake pressure. Furthermore, based on thegenerally known prior art in traction control technology, there is thepossibility of using the vehicle brake system for compensation forexcess drive torque in vehicle wheels by controlling the first andsecond valves.

The features set forth herein produce the advantage that on the onehand, when the wheel brake pressure is increased and/or kept constant, apreceding and disadvantageous pressure fluid discharge to the reservoirby means of the second valve is prevented and that on the other hand, asa result of a total pressure difference between the external energysource or its pump and the reservoir, which pressure difference can bejointly adjusted by means of the first valve and the second valve, theexternal energy source or its pump or other elements can be protectedagainst overloading. According to the modulation of the secondexcitation current controller or the regulator that acts on the secondexcitation current controller, the pressure prevailing in the externalenergy source is then only a few bar higher than when the brake pedal isreleased and the second valve is therefore opened, wherein according tothe invention, the first valve fulfills the function of a pump pressureregulating valve. Other features disclose an advantageous embodiment ofthe control device.

BRIEF DESCRIPTION OF THE DRAWINGS

Two exemplary embodiments of the hydraulic motor vehicle power brakesystem according to the invention are depicted in the drawings andexplained in detail below.

FIG. 1 shows the hydraulic circuit of a first exemplary embodiment ofthe hydraulic motor vehicle power brake system,

FIG. 2 shows the circuit diagram of a second exemplary embodiment of themotor vehicle power brake system according to the invention,

FIG. 3 shows a circuit diagram for a control device of the motor vehiclepower brake system according to the invention, and

FIG. 4 shows an exemplary wheel brake pressure progression during aperiod of time and excitation currents that are associated with it andpertain to a first and second valve of the hydraulic motor vehicle powerbrake system according to FIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The first exemplary embodiment of a hydraulic motor vehicle power brakesystem 2 according to FIG. 1 has an external energy source 3, 4, a firstvalve 5, a second valve 6, at least one wheel brake 7 and one wheelbrake pressure sensor 8 connected between the first valve 5 and thesecond valve 6, a wheel brake pressure set-point transmitter 9, a brakepedal. 10 for adjusting the wheel brake pressure set-point transmitter9, and a control device 11.

In the exemplary embodiment of FIG. 1, the external energy source 3, 4is comprised of a pump 12, an electromotor 13 to drive the pump 12, anexternal energy reservoir 14 embodied as a hydraulic accumulator, apressureless reservoir 15 for hydraulic pressure fluid, and a pumppressure sensor 16. An inlet 17 of the pump 12 is connected to an intakeline 18, whose front end 19 dips into the reservoir 15. By means ofpressure lines 21 and 22, an outlet 20 of the pump 12 supplies thehydraulic accumulator 14 being used to store the external energy, whichaccumulator can be embodied, for example, as a so-called bladderreservoir with a gas buffer. By means of another pressure line 23, thepump pressure sensor 16 can be connected to the pressure line 21 andtherefore to the outlet 20 of the pump 12. Starting from the pressureline 21, a pressure line 24 leads from the external energy source 3 tothe first valve 5.

The first valve 5 has a housing 25 with an inlet opening 26 and anoutlet opening 27. The inlet opening 26 feeds into a valve seat 28. Thevalve seat 28 is associated with a closing body 29. For example, theclosing body 29 is embodied as ball-shaped in a region designated forcontacting the valve seat 28. The valve 5 also has a closing spring 30that presses the closing body 29 against the valve seat 28. In a manneraccording to the invention, this closing spring 30 is embodied andprestressed matched to the diameter of the valve seat 28 in such a waythat it assumes the function of a safety valve spring and when the pump12 is running, limits its pressure or when the pump 12 is inactive andthere is a temperature increase in the hydraulic accumulator 14,prevents a disadvantageous pressure increase. The valve 5 can beelectromagnetically controlled and to this end, has at least one excitercoil 31 and one armature 32. A wheel brake line 33 leads from the outletopening 27 of the valve 5 and leads to the at least one wheel brake 7 orit branches. The wheel brake pressure sensor 8 is connected to the wheelbrake line 33 by means of a sensor line 34 and therefore communicateswith the at least one wheel brake 7. Another wheel brake line 35communicates with the at least one wheel brake 7.

The second valve 6 likewise has a housing 36, an inlet opening 37, andan outlet opening 38. The inlet opening 37 is connected to the wheelbrake line 35 and therefore communicates with the at least one wheelbrake 7 and the wheel brake pressure sensor 8. The inlet opening 37feeds into a second valve seat 39. The second valve seat 39 isassociated with a second closing body 40. Furthermore, the valve 6 hasan opening spring 41, which is capable of opening the valve 6, but isdimensioned to be as weak as possible. In order to electromagneticallycontrol the valve 6, it is associated with at least one excitation coil42 and an armature 43.

So that the following function description of the hydraulic motorvehicle power brake system 2 is simple and clear, the valve seat 39should, for example, have the same diameter as the valve seat 28 of thefirst valve 5 mentioned. Also, the closing body 40 of the second valve 6should be embodied identically to the closing body 29 of the first valve5.

A return line 44 leads from the outlet opening 38 of the second valve 6and feeds into the reservoir 15.

The control device 11, whose structure will be explained later inconjunction with FIG. 3, is connected on the one hand to the wheel brakepressure sensor 8 and on the other hand, is connected to the wheel brakepressure set-point transmitter 9. Furthermore, the control device 11 isalso connected to the pump pressure sensor 16. Electrical lines 45, 46,47 lead from the control device 11. The line 45 leads to theelectromotor 13 of the pump 12. The electrical line 46 leads to theexcitation coil 31 of the first valve 5, and the electrical line 47leads to the excitation coil 42 of the second valve 6. In anticipationof the description of FIG. 3, the control device 11 has a firstexcitation current controller 48, which is connected to the electricalline 46, and has a second excitation current controller 49, which isconnected to the electrical line 47.

Analogous to the embodiment of the valve seat 39 of the second valve 6for example identically to the valve seat 29 of the first valve 5, theexcitation coil 42 of the second valve 6 is embodied identically to theexcitation coil 31 of the first valve 5. The same is true for thearmature 43 with regard to magnetic properties.

Mode of Operation of the Hydraulic Motor Vehicle Power Brake System 2

The control device 11 receives a signal from the pump pressure sensor 16and as a result, recognizes whether the hydraulic accumulator 14 issufficiently filled or whether it should be filled by switching on theelectromotor 23 and therefore driving the pump 12. In the example, itdoes not intrinsically matter whether the pump pressure sensor 16 isembodied simply as a pressure switch comparable to the one in DE 19 61039 A1 or whether the pump pressure sensor 16 sends a signalproportional to the pressure generated by the pump 12, which signal cancorrespondingly proportional p underlying a proportional power supply ofthe electromotor 13.

If the brake pedal 10 is not being actuated, then the wheel brakeset-point transmitter 9 is set to "brake pressure zero" and the controldevice 11 produces the "excitation current intensity zero" in theexcitation current controllers 48 and 49. Accordingly, the second valve6 is disposed in the open position shown and the first valve 5 is in theclosed position shown. The open position of the second valve 6 leads tothe fact that the at least one wheel brake 7 communicates with thereturn line 44 and is therefore pressureless. In contrast, the closingspring 30 of the first valve 5 loads the closing body 29 indirectly viathe armature 31 and inside the valve seat 28, the closing body issubjected on the one hand to the pressure of the external energy source3 and on the other hand, is subjected to a resultant axial component ofan opposing force possibly produced by the valve seat 28. If thepressure in the hydraulic accumulator 14 threatens to rise in animpermissible manner, either as the result of an inadequate function ofthe pump pressure sensor 16 or the control device 11 or due to theheating of the hydraulic accumulator 14 when the pump 12 is inactive,then an axial force pressing on the closing body 29 due to the crosssection of the valve seat 28 as a function of the existing pressureprevails over the force of the spring 30, which is embodied according tothe invention as a safety spring, resulting in the fact that due to thelifting of the closing body 29 from the valve seat 28, pressure fluidflows through the inlet opening 26 and the outlet opening 27 of thefirst valve 5 and finally discharges into the pressure free reservoir 15through the open second valve 6 and the return line 44. In this respect,it is clear that the embodiment of the first valve 5 according to theinvention, at least when the brake pedal 10 is not being actuated,permits the elimination of an otherwise standard separately installedsafety valve.

If the actuation of the brake pedal adjusts the wheel brake pressureset-point transmitter 9 so that the control device 11 receives a brakepressure set point that can be arbitrarily set by the driver, but thewheel brake pressure "zero" is still sent by means of the wheel brakepressure sensor 8, then the control device 11 controls the secondexcitation current controller 49 in such a way that due to the resultantexcitation current flowing through the electrical line 47, theexcitation coil 42 produces a magnetic field and as a result, pressesthe armature 43 counter to the force of the opening spring 41 in theclosing body 40 onto the valve seat 39 of the second valve 6.Furthermore, the control device 11 also controls the first excitationcurrent controller 48 so that the excitation coil 31 produces a magneticfield that acts on the armature 32 so that it compensates for at leastpart of the closing force of the closing spring 30. This has the desiredresult that only a part of the closing force of the closing spring 30 isavailable for pressing the closing body 29 against the valve seat 28and/or as a force counter to a hydraulic load with the force of theexternal energy source 3 multiplied by the cross section of the valveseat 28. The excitation of the excitation coil 31 therefore at leasttemporarily produces an imbalance of force which leads to the departureof the closing body 29 from the valve seat 28 and as a result leads to aflow of pressure fluid through the pressure line 24, the inlet opening26, the housing 25, the outlet opening, 27, and the wheel brake line 33into the at least one wheel brake 7, with the result that in the atleast one wheel brake 7, a wheel brake pressure increase is produced andas a result, an initially existing pressure difference between the inletopening 26 and the outlet opening 27 of the first valve 5 becomessmaller until finally, due to the resultant downstream hydraulicimpingement of the closing body, the closing spring 30 is in a positionto seal the valve seat 28 by means of the closing body 29. The increasedpressure leading up to the sealing in the wheel brake 7 also acts bymeans of the sensor line 34 in the wheel brake pressure sensor 8, whichsends an actual signal to the control device 11, which signal isassociated with the wheel brake pressure sensed. In a manner that willbe described later in conjunction with FIG. 3, the control device 11 isembodied in such a way that it increases a possibly insufficientlyincreased wheel brake pressure actual value by means of intensifiedcontrol of the first excitation current controller 48. The controldevice 11 is also equipped in such a way that in association with thewheel brake pressure set point chosen by the driver, the secondexcitation current controller 49 supplies an excitation current to theexcitation coil 42, which current maintains a wheel brake pressure inthis wheel brake 7 that corresponds to at least the magnitude of thewheel brake pressure set point.

It is clear that when the second valve 6 is closed in a sufficientlyfirm manner, a wheel brake pressure increases more sharply the moreintensely the excitation current coming from the first excitationcurrent controller 48 is adjusted. However, it is also clear that for ahigh wheel brake pressure, the second valve 6 must be kept closed bymeans of a greater excitation current from the second excitation currentcontroller 49 than when there is a relatively low wheel brake pressure.

If the driver arbitrarily uses the brake pedal 10 to adjust the brakepressure set-point transmitter 9 to a lower brake pressure set point,then the control device 11 recognizes that the brake pressure actualvalue that is sent from the brake pressure sensor 8 to the controldevice 11 is higher. Therefore by a weakened control of the secondexcitation current controller 49, the control device 11 reduces theclosing force in the second valve 6 so that the second valve 6 can beused to discharge pressure fluid from the wheel brake 7 to the reservoir15. At the same time, the control device 11 also acts on the firstexcitation current controller 48 to a weakened degree so that a pressuredifference that possibly exists between the inlet opening 26 and theoutlet opening 27 of the first valve 5 can become greater. If the driverarbitrarily allows the brake pedal 10 to return to its initial position,then the wheel brake pressure set-point transmitter 9 sends the "wheelbrake pressure zero" to the control device 11 so that this controldevice acts on both excitation current controllers 48 and 49 in such away that they no longer emit excitation current. This brings theapparatus back to the state from which the function description began.

An exemplary embodiment of the control device 11 is described below inconjunction with FIG. 3.

The control device 11 has a first input 50, a second input 51, and athird input 52. The first input 50 is connected to the wheel brakepressure sensor 8. The second input 51 is connected to the wheel brakepressure set-point transmitter 9. The control device 11 has a fourthinput 53 for the power supply.

For example, the first input 50 is connected to a first input 54 of acomparator 55. This comparator 55 has a second input 56 as well as anoutput 57 and is for example embodied in a manner associated with theprior art and therefore need not be described in detail. An adaptor unit58 is connected to the second input 51 of the control device 11 and iselectrically connected to the second input 56 of the comparator 55. Inthe example, the comparator 55 is equipped to process actual signalscoming from the wheel brake pressure sensor 8. As a result of thedisposition of the adaptor unit 58, depending on how the wheel brakepressure set-point transmitter 9 is embodied, signals sent from thewheel brake pressure set-point transmitter 9 can be adapted to theorderof magnitude, for example to the level of signals that can be sentfrom the wheel brake pressure sensor 8 and/or to the type of signal thatthe wheel brake pressure set-point transmitter 8 can deliver. In otherwords, voltages, for example, which are proportional to a wheel brakepressure supplied to the wheel brake pressure sensor 8, can be deliveredto the input 50 of the control device 11. In contrast to this, the wheelbrake pressure set-point transmitter 9, for example, can be embodied inaccordance with the prior art for the purpose of sending digitally-codedbrake pressure set points. In one such instance, the adaptor unit 58 isembodied as a digital-analog converter so that at both inputs 54 and 56,the comparator 55 receives analog signals with levels that are modulatedto each other.

If the signal magnitudes at the first input 54 and the second input 56differ from each other, then the difference appears at the output 57.

A differentiator 59 is connected directly to the wheel brake pressureset-point transmitter 9 or, as shown in FIG. 3, is connected to theadaptor unit 58 on the output end. In the adaptation to analog signals,for example, which are sent by the adaptor unit 58, the differentiatoris an analog differentiator whose essential element is a capacitor, notshown, and a measurement circuit, not shown. This measurement circuit isembodied, for example, so that it carries a signal "brake pressureincrease" at an output 61 when there are analog signals of increasingsize coming from the adaptor unit 58, which signals lead to a chargingof the capacitor. Conversely, the measurement circuit is equipped insuch a way that with "reduce brake pressure", a signal is sent from anoutput 60 of the differentiator 59. This signal from the output 60 issupplied to a first regulator 62 that is connected to the firstexcitation current controller 48. A signal "increase brake pressure"from the output 61 is supplied to a second regulator 63 that isconnected to the second excitation current controller 49. The signalscoming from the outputs 60 and 61 are used for converting the tworegulators 62 and 63 respectively from a first controllingcharacteristic curve to a second controlling characteristic curve. Asignal from the pump pressure sensor 16 is supplied by means of theinput 52, for example as an additional variable that acts on theregulators 62 and 63.

The fourth input 53 of the control device 11 is connected, for example,to a battery 64 of a motor vehicle. Because it is known that batteries64 of the kind in question do not emit constantly high voltages,particularly when under different loads, a regulated voltage converter65 is connected to the fourth input 53, which can be inferred from theprior art and therefore does not need to be described. The voltageconverter 65 supplies power to at least the two regulators 62 and 63and, in a manner not shown, also powers the excitation currentcontrollers 48 and 49, for example, which are embodied, for example, inthe form of controllable current regulators.

In the control device 11, a pump control device or pump regulator device66 is connected to the third input 52 and consequently to the pumppressure sensor 16. The pump control device 66 is used for controlling amotor current controller 67 in such a way that it supplies theelectromotor 13 with current by means of the line 45 in order to drivethe pump 12, so that this pump charges the hydraulic accumulator 14 bymeans of the line 21. It cannot be prevented that when the hydraulicaccumulator 14 is being charged, a pressure change occurs in the line 21and therefore also in the inlet opening 26 of the first valve 5. This isthe reason why the pump pressure sensor 16, as described above, can beconnected to the two regulators 62 and 63. The two regulators 62 and 63are then equipped in a manner not shown so that they recognize pressureprogressions sent by the pump pressure sensor 16 as pressurefluctuations and take them into account when carrying out theregulation. This is therefore advantageous because in order to achieve awheel brake pressure desired by the driver, the lower the externalenergy pressure that is generated by the pump 13 or is currently presentin the hydraulic accumulator 14, the more intense an excitation currentmust be supplied by the excitation current controller 48 to the firstvalve 5.

It has already been mentioned that the two regulators 62 and 63 can beembodied in a manner that is intrinsically arbitrary. In the event thatthe analog comparator 55 described is used, the two regulators 62 and 63are preferably embodied as analog regulators. However, it is alsopossible to use a digital comparator in lieu of an analog comparator 55,or a computer, not shown, inside the control device 11, using softwarestored in the computer to compare input variables of set points andactual value to one another by computation and to digitally supply thedeviations to the regulators 62 and 63. The regulators 62 and 63themselves are in this instance also represented by means of a computerand are operated using software stored in the computer. Acontinuous-time regulation or a time-discrete regulation can take placedepending on a selected structure and the technical embodiment of thecomputer.

Regardless of which type it is embodied as, the first regulator 62 has afirst regulating characteristic curve, which is used to increase brakepressure and a second characteristic curve that is effective duringbrake pressure reduction. The second regulator 63 also has a firstcharacteristic curve and a second regulating characteristic curve, butin this instance, the first curve is effective during a brake pressuredecrease and the second curve is accordingly effective during a brakepressure increase.

Mode of Operation of the Control Device 11

When the brake pedal 10 is released, the comparator 55 receives signalsof the same intensity at both inputs 54 and 56, which signalscorrespond, for example, to the brake pressure value "zero".Accordingly, no difference signal is apparent at the output 57. When thebrake pedal 10 is released, no set-point change occurs so that nocontrol signals are apparent at the outputs 60 and 61 of thedifferentiator 59. Independent of this and as a function of a signalthat originates from the pump pressure sensor 16, which signal dependson whether the pump pressure lies above or below a predeterminedpressure, the pump control device 66, by means of the motor currentcontroller 67, makes sure that a current is supplied to the electromotor13 so that the electromotor 13 drives the pump 12 in order to increasean insufficient pump pressure to the desired measure.

If the brake pedal 10 is actuated by a driver, then the wheel brakepressure set-point transmitter 9 sends this set point to the adaptorunit 58. In the manner described above, the adaptor unit 58correspondingly sends a signal, which is associated with the set point,to the second input 56 of the comparator 55. Because for the time beingno wheel brake pressure is present in the at least one wheel brake 7,there will also correspondingly be an actual value at the first input 54of the comparator 55, which actual value is insufficient in relation tothe set point, which results in the fact that the comparator 55 sendsthe deviation to the first regulator 62 and the second regulator 63 bymeans of the output 57 in a manner mentioned above. The switching of thesecond regulator 63 over to the second regulating characteristic curvealso goes along with the production and increase of a wheel brakepressure set point 9.

The first regulator 62 is equipped in such a way that by using its firstcharacteristic curve, it uses the initial variable, which corresponds tothe given difference, as a signal for increasing brake pressure up tothe wheel brake pressure set point. The regulator 62 is therefore set toa higher excitation current at the first excitation current controller48, the higher the wheel brake pressure set point is chosen by thedriver. The wheel brake pressure sensor 8 sends the controller result,which is detected by the wheel brake pressure sensor 8, to the firstinput 54 of the comparator 55. Accordingly, a difference signal that wasinitially present at the output 57 becomes smaller and the regulator 62ends the adjustment of the first excitation current controller 48 andmaintains the adjustment achieved.

At the same time, the second regulator 63 is operated with its secondcharacteristic curve. The second characteristic curve of the secondregulator 63 is characterized in that with an "increase brake pressure"tendency display coming from the output 61 of the differentiator 59,this regulator 63 controls the second excitation current controller 49in such a way that for a particular wheel brake pressure, this secondexcitation current controller 49 carries a superelevated excitationcurrent to the second valve 6. As a result, the second valve 6 isprevented from opening in an undesirable manner when the brake pressureincreases and partial quantities of pressure fluid, which should flowthrough the first valve 5 in the direction of at least one wheel brake 7to increase brake pressure, are prevented from flowing into thereservoir 15 and not into this wheel brake 7. It is also once more clearin this connection that the assurance against undesirable discharge ofpressure fluid from the external energy source 3 is more reliablyprevented the more forcefully the second valve 6 is held closed by meansof excitation current from the second excitation current controller 49.Here too, though, the second valve 6 should not be held closed toostrongly, because otherwise when the pump 12 supplies excess pressurefluid, an undesirable wheel brake pressure increase occurs, whichresults in an increased brake function, which the driver can in factcompensate for by partially releasing the brake pedal 10, but has thepotential to be very disadvantageous when the roadway is icy. The secondregulator 63 in this instance is also equipped in such a way that anexcess of closing force in the second valve 6 is not too great. Thiskind of excess closing force can also be eliminated more rapidly when,by means of its output 57, the comparator 55 sends the regulatingdeviation "wheel brake pressure too high" to the second regulator 63.

The respective difference between an excitation current intensity whenincreasing to a particular wheel brake pressure or when de creasing to aparticular wheel brake pressure can therefore be selected, for example,in the form of an essentially constant difference magnitude or in theform of a pre-selected factor so that at higher brake pressures, greaterdifferences in the excitation currents can also result. The latter canbe advantageous if the disturbance variables mentioned are relativelygreat. It is relatively insignificant that at low wheel brake pressures,pressure fluid, which is intrinsically unused, is possibly dischargedfrom the external energy source 3 to the reservoir 15, because only apart of the pump capacity and the "normal pressure" projected for theexternal energy source 3 is required to produce low wheel brakepressures.

In the top third, FIG. 4 shows an arbitrary example for a wheel brakepressure progression over time. Since this progression is a result ofactuating the brake pedal 10 and therefore adjusting the wheel brakepressure set-point transmitter 9, the progression is labeled 90. Theprogression 90 begins sometime when the wheel brake pressure is "zero"and ends in the example at time t8, likewise when the wheel brakepressure is "zero". A first current increase 90.1 is affiliated with afirst electrical current increase 31.1 for the excitation coil 31, whichincrease is shown in the middle third of FIG. 4. In association with thecurrent increase 31.1 controlled by the first regulator 62, the secondregulator 63 first generates a current jump 42.1, which is for exampleadjoined by a current increase 42.1a for the excitation coil 42 of thesecond valve, which increase is steeper in comparison to the currentincrease 31.1. In this instance, therefore, use is made of bothpreviously mentioned possibilities of superelevating the closing forceof the second valve 6 when producing a brake pressure increase. In thetop third of FIG. 4, the brake pressure increase 90.1 is adjoined by awheel brake pressure retention phase, which is indicated by a horizontalline 90.2. This permits no change to the current intensities whichbrought about the first brake pressure increase. A second pressureincrease 90.3 adjoins this, which requires another current increase 31.3according to the middle third of FIG. 4. A current increase that islabeled 42.3 is also required in the excitation coil 42 of the secondvalve 6. The second brake pressure increase 90.3 also adjoins a firstpartial brake pressure decreasing process 90.4. So that this can takeplace, an excess of closing force in the second valve 6 must beeliminated, which is represented by a very steep current drop 42.4, i.e.a negative current jump, and an essentially steady reduction inexcitation current intensity 42.4a adjoining this. During this process,there should be an excess of closing force in the first valve 5, whereinthis excess of closing force is indicated in the middle third of FIG. 4by the relatively slightly inclined excitation current progression 31.4.This partial brake pressure reduction is adjoined by a brake pressureretention phase, which is represented by a constant current by means ofa straight line 42.5 between the times t4 and t5. Since during this kindof pressure retention phase, it can be expected that the pump 12supplies an excess of pressure fluid, it is desirable that this pressurefluid excess reaches the reservoir 15 without significant pressurechange in the external energy source 3. To this end, the excitationcurrent for the excitation coil 31 can be reduced somewhat between thetimes t4 and t5, which is characterized in the middle third of FIG. 4 bya slightly inclined straight line 31.5 between the times t4 and t5.Starting at the time t5, a subsequent third brake pressure increase 90.6can in principle be produced in the same manner as the second brakepressure increase 90.3 since a brake pressure retention phase is thestarting point in both instances. A third brake pressure retention phase90.7 that adjoins this does not have to be described because here too,there is a transition from an increase phase into a retention phase inthe same way that this occurred at the transition of the first brakepressure increase 90.1 into the first brake pressure retention phase90.2. A subsequent wheel brake pressure reduction 90.8 to the value zeropresupposes a complete closing of the first valve 5 and accordingly, anexcitation current progression 31.8 to the reference value "zero". Sothat a first opening procedure of the second valve 6 can take place inthe presence of the wheel brake pressure prevailing at the beginning ofthe brake pressure decreasing procedure, a jump-like initial currentdecrease 90.8 occurs, which is adjoined by an inclined current decrease42.8a down to the value zero.

As already mentioned in the introduction to the specification and as hasalready been disclosed by U.S. Pat. No. 3,802,745, with regard to brakedvehicle wheels in which the danger of wheel locking occurs to differentdegrees, in order to be able to be able to automatically brake theindividual vehicle wheels in a manner that depends on the conditions,for example for four vehicle wheels, four first valves 5, 5.1, 5.2, 5.3and four second valves 6, 6.1, 6.2, and 6.3 can be provided for fourwheel brakes 7, 7.1, 7.2, and 7.3. For this, a vehicle wheel, not shown,to be braked by the wheel brake 7 is associated with a wheel rotationsensor 70 and is electrically connected to the control device 11.1 thathas been modified for automatic brake slip regulation. Because thismodification is carried out based on the prior art, three wheel brakes7.1, 7.2, and 7.3 of the other vehicle wheels are associated with threeother wheel rotation sensors 70.1, 70.2, 70.3.

For the hydraulic motor vehicle brake system 2a shown in FIG. 2, whichhas the control device 11.1 that is modified to prevent the danger ofwheel locking, preferably use is made of the regulating characteristiccurve for the second regulator 63, which operates for jump-like increaseof excitation current at the start of a braking and for a jump-likeexcitation current adaptation when a brake pressure reduction isinitiated. This produces the advantage that when there are slightchanges in brake pressure, which can occur, for example, in the antilockoperation, and with the steady consumption of pressure fluid from theexternal energy source 3 required by this, an above-mentioned wastefuldischarge of pressure fluid from the external energy source into thereservoir can be sufficiently prevented.

In the simplification already described above, which states that thevalve seats 28 and 39 and also the excitation coils 31 and 42 areembodied as structurally equivalent and the electromagnetic propertiesof the armature 32 and 43 practically coincide, it can therefore besummarily established that during a brake pressure regulating operation,i.e. with the increase of wheel brake pressure by pressing down on thebrake pedal 10 and with the decrease of wheel brake pressure byreleasing the brake pedal 10, an excitation current of the excitationcoil 31 of the first valve 5 can essentially be just the same as anexcitation current for the second excitation coil 42 of the second valve6. Deviations from this are produced by means of undesirably low pumppressure, whose disturbance variable Z1 is characterized in FIG. 3, andby means of the characteristic curves of the first regulator 62 whenbrake pressure decreases and of the second regulator 63 when brakepressure increases.

Up to this point, it has been assumed that the valve seats 28 and 39 arestructurally equivalent. If a deviation from this structural equivalenceoccurs, naturally deviations also occur in such a manner that the valveseat that is embodied as larger requires greater closing forces andcorrespondingly, an associated excitation coil must be more powerful.For example, the larger valve seat can be associated with a second valveso that a wheel brake pressure that is already intrinsically low can berapidly reduced, for example when driving on an icy roadway. In a caselike this, therefore, the first respective valve has the narrower valveseat, which does not have to be disadvantageous because rapid wheelbrake pressure increases can be generated through a narrow valve seat aswell, by means of the relatively high pressure of the external energysource 3, and because excessively rapid wheel brake pressure increasesimpair the antilock operation.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A hydraulic motor vehicle power brake system comprising areservoir for hydraulic pressure fluid, an external energy source thatis supplied from the reservoir, said external energy source includes apump driven by a motor and at least one means for limiting the pressureof the pump, at least one valve device disposed between the externalenergy source and at least one wheel brake as well as the reservoir,said valve device is electrically controlled and has at least one springand is for separating the wheel brake from the reservoir and forconnecting the wheel brake to the external energy source, a wheel brakepressure sensor associated with the wheel brake, a brake pedal and anelectrical set-point transmitter that is adjusted by means of said pedaland is for selecting a wheel brake pressure, a control device connectedto the set-point transmitter and the wheel brake pressure sensor, saidcontrol device is equipped for comparing signals from the set-pointtransmitter and the wheel brake pressure sensor and for electricallycontrolling the valve device as a function of a comparison result, afirst and second valve device (5, 6) embodied in accordance with a seatvalve construction, said first valve device has a valve seat (28)connected to the external energy source (3) and a closing body (29) thatis pressed against the valve seat (28) by the spring (30), the spring(30) is dimensioned as a safety valve spring, the first valve device (5)has at least one electromagnet (31, 32) which counteracts a force of thespring (30) when an excitation current is supplied by the control device(11, 48), and that the control device (11) has an excitation currentcontroller (48) which is connected to the electromagnet (31, 32).
 2. Ahydraulic motor vehicle power brake system according to claim 1, inwhich the second valve device (6) has a second valve seat (39) connectedto the wheel brake (7) and associated with said wheel brake, said secondvalve device has a second closing body (40) as well as a secondelectromagnet (42, 43), which is associated with the second closing body(40) and is for loading the second closing body (40) in the closingdirection in opposition to possibly existing wheel brake pressure, andthat the control device (11) has a second excitation current controller(49) and is modified for controlling the second excitation currentcontroller (49) to adjust wheel brake pressure at least during a wheelbrake pressure decreasing procedure.
 3. A hydraulic motor vehicle powerbrake system according to claim 2, in which the valve seat (28) of thefirst valve (5) and the valve seat (31) of the second valve (6) areessentially embodied as structurally equivalent and that the controldevice (11) is equipped to control the excitation current of the secondelectromagnet (42, 43) at least in a manner that directionally dependson the first excitation current, in such a way that during a brakingoperation, both excitation currents have essentially the same intensity.4. A hydraulic motor vehicle power brake system according to claim 3, inwhich the hydraulic motor vehicle brake system (2a) has at least oneadditional valve device (5.1, 5.2, 5.3, 6.1, 6.2, 6.3) and at least onefirst additional excitation current controller (48) and at least oneadditional second excitation current controller (49).
 5. A hydraulicmotor vehicle power brake system according to claim 3, in which thewheel brake pressure set-point transmitter (9) and the at least onewheel brake pressure sensor (8) are connected to a comparator (55) thathas an output (57), that the output (57) of the comparator (55) isconnected to a first regulator (62) that acts on the first excitationcurrent controller (48) and a second regulator (63) that acts on thesecond excitation current controller (49), wherein the first regulator(62) is equipped in such a way that when a set point is changed, itemits a greater excitation current when there is a brake pressuredecrease than when there is a brake pressure increase, and wherein thesecond regulator (63) is equipped in such a way that when there is abrake pressure increase during a brake pressure decrease, the secondregulator (63) eliminates an excess closing force in the second valve(6).
 6. A hydraulic motor vehicle power brake system according to claim5, in which the wheel brake pressure set-point transmitter (9) isconnected to a differentiator (59) which, based on a change of a signalcoming from the wheel brake pressure set-point transmitter (9),indicates "brake pressure increase" or "brake pressure decrease" on atleast one output (60, 61), in order to switch the first regulator (62)and the second regulator (63) over to controlling the excitation currentcontrollers (48, 49) for brake pressure increases or brake pressuredecreases.
 7. A hydraulic motor vehicle power brake system according toclaim 2, in which the hydraulic motor vehicle brake system (2a) has atleast one additional valve device (5.1, 5.2, 5.3, 6.1, 6.2, 6.3) and atleast one first additional excitation current controller (48) and atleast one additional second excitation current controller (49).
 8. Ahydraulic motor vehicle power brake system according to claim 2, inwhich the wheel brake pressure set-point transmitter (9) and the atleast one wheel brake pressure sensor (8) are connected to a comparator(55) that has an output (57), that the output (57) of the comparator(55) is connected to a first regulator (62) that acts on the firstexcitation current controller (48) and a second regulator (63) that actson the second excitation current controller (49), wherein the firstregulator (62) is equipped in such a way that when a set point ischanged, it emits a greater excitation current when there is a brakepressure decrease than when there is a brake pressure increase, andwherein the second regulator (63) is equipped in such a way that whenthere is a brake pressure increase during a brake pressure decrease, thesecond regulator (63) eliminates an excess closing force in the secondvalve (6).
 9. A hydraulic motor vehicle power brake system according toclaim 8, in which the wheel brake pressure set-point transmitter (9) isconnected to a differentiator (59) which, based on a change of a signalcoming from the wheel brake pressure set-point transmitter (9),indicates "brake pressure increase" or "brake pressure decrease" on atleast one output (60, 61), in order to switch the first regulator (62)and the second regulator (63) over to controlling the excitation currentcontrollers (48, 49) for brake pressure increases or brake pressuredecreases.
 10. A hydraulic motor vehicle power brake system according toclaim 1, in which the hydraulic motor vehicle brake system (2a) has atleast one additional valve device (5.1, 5.2, 5.3, 6.1, 6.2, 6.3) and atleast one first additional excitation current controller (48) and atleast one additional second excitation current controller (49).
 11. Ahydraulic motor vehicle power brake system according to claim 10, inwhich the wheel brake pressure set-point transmitter (9) and the atleast one wheel brake pressure sensor (8) are connected to a comparator(55) that has an output (57), that the output (57) of the comparator(55) is connected to a first regulator (62) that acts on the firstexcitation current controller (48) and a second regulator (63) that actson the second excitation current controller (49), wherein the firstregulator (62) is equipped in such a way that when a set point ischanged, it emits a greater excitation current when there is a brakepressure decrease than when there is a brake pressure increase, andwherein the second regulator (63) is equipped in such a way that whenthere is a brake pressure increase during a brake pressure decrease, thesecond regulator (63) eliminates an excess closing force in the secondvalve (6).
 12. A hydraulic motor vehicle power brake system according toclaim 11, in which the wheel brake pressure set-point transmitter (9) isconnected to a differentiator (59) which, based on a change of a signalcoming from the wheel brake pressure set-point transmitter (9),indicates "brake pressure increase" or "brake pressure decrease" on atleast one output (60, 61), in order to switch the first regulator (62)and the second regulator (63) over to controlling the excitation currentcontrollers (48, 49) for brake pressure increases or brake pressuredecreases.